Mechanical refrigeration systems, and related heat transfer devices such as heat pumps and air conditioners, using refrigerant liquids are well known in the art for industrial, commercial and domestic uses. Chlorofluorocarbons (CFCs) were developed in the 1930s as refrigerants for such systems. However, since the 1980s the effect of CFCs on the stratospheric ozone layer has become the focus of much attention. In 1987 a number of government signed the Montreal Protocol to protect the global environment setting forth a timetable for phasing out the CFC products. Subsequent amendments to this protocol accelerated the phase-out of these CFCs and also scheduled the phase-out of HCFCs. Thus, there is a requirement for a non-flammable, non-toxic alternative to replace these CFCs and HCFCs. In response to such demand industry has developed a number of hydrofluorocarbons (HFCs), which have a zero ozone depletion potential.
Hydrofluorcarbons such as difluoromethane (HFC-32), 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,2,2-pentafluoroethane (HFC-125a) have essentially no ozone depletion potential (ODP) and therefore, they have been found to be acceptable refrigerants and, in some cases, as potential blowing agents in the production of plastic foams, as cleaning solvents and as propellants for aerosol sprays.
A number of processes are known for producing the desired HFC compounds. One such process involves the catalytic hydrogenation of CFC compounds in the presence of hydrogen gas. However, safety related issues associated with handling of hydrogen gas in a large scale production is always a major concern. Additionally, hydrogenation of CFCs to HFCs is often a very non-selective reaction because of the reactivity of the fluorine group with hydrogen. Such process can also involve the production of toxic chlorinated by-products. Moreover, such reactions have generally required the use of expensive catalysts, e.g., Group IB catalysts such as silver or gold catalysts, Group VIII catalysts, such as platinum or palladium catalysts, or lanthanum or lanthanide element catalysts. Example of such processes can be found for example in European Patent publications 0 347 830 and 0 508 660, PCT Patent publications WO 92 12113, WO 94 11328, WO 96 17683 A1, and WO 96 16009 A2, and U.S. Patent publication U.S. 2004167366 A1.
There is therefore a need for an improved process or synthesis method for the production of HFCs from HCFCs or CFCs that would not require the use of hydrogen gas and that is highly selective for the desired HFCs. A further need is for a improved process or synthesis method that is relatively simple to perform and can produce high conversion, up to 100% conversion, of the HCHC or CFC reactants. It would also be desirable to have such a process for conversion of HCFCs or CFCs to HFCs that can use, but does not require the use of, expensive metal catalysts, but can instead employ relatively inexpensive metal catalysts.